1. Field of the Invention
This invention relates to a method and apparatus for separating slag and pouring molten steel out of a container such as a converter or the like, which can efficiently pour the molten steel only out of the container without degrading the yield of the molten steel.
2. Description of the Prior Art
In the case of pouring molten steel out of a converter after a refining has been completed, slag is often mixed into the molten steel during its pouring and particularly at the end thereof. In general, it is difficult to eliminate such drawback. The slag mixed into the molten steel degrades the yield of alloy material and promotes the erosion of ladle refractories. In addition, there is a risk of the quality of steel being deteriorated. Moreover, the slag mixed into the molten steel causes the concentration of phosphorus in the molten steel to increase.
As a result, it is most important to prevent the slag from pouring into the ladle at the tapping. Many attempts have been made to overcome this problem, but hitherto none has led to fully satisfactory results owing to the following reasons.
A conventional method of using an open and closing device such as a sliding gate or the like provided at the tapping hole of the converter can prevent the slag from mixing into the molten steel, but has the disadvantage that the yield of the molten steel becomes degraded and that the maintenance of the open and closing device applied to a large converter is difficult.
Another conventional method of using a ladle provided therein with a slag pot and of collecting the slag therein has the disadvantage that the temperature drop of the molten steel is large. In order to obviate such disadvantage a slag stop ball has generally been used or after the molten steel has been poured the flow of molten steel is deviated from the ladle, that is use has been made of a so-called ladle cut or the like. The latter two methods are easy in operation, but lack in reliability.
In order to avoid such drawback, the following apparatus for separating slag and pouring molten steel out of a container such as a converter or the like has been proposed. This apparatus comprises a container for containing molten metal and slag covering the free surface of the molten metal, a U-shaped passage composed of a descending portion communicated with a tapping hole of the container, an intermediate portion and an ascending portion communicated with an outlet opening of the U-shaped passage and secured to and located at the lower side portion of the container when it is tilted into its molten steel pouring position after the refining has been completed, the U-shaped passage being operative to keep the static pressure of the residual molten steel in balance with the static pressure of the residual slag therein.
This apparatus is based on the following basic idea.
The condition under which the static pressure of the residual molten steel in the U-shaped passage is kept in balance with the static pressure of the residual slag flowing after the molten steel and also remaining in the U-shaped passage so as to prevent the slag from flowing out of the U-shaped passage is given by the following formula (1). EQU h.sub.2 .rho..sub.m &gt;(h.sub.1 +h.sub.s).rho..sub.s ( 1)
where .rho..sub.m is a molten steel density, .rho..sub.s is a slag density, h.sub.1 is a height of the descending portion of the U-shaped passage, h.sub.2 is a height of the ascending portion of the U-shaped passage and h.sub.s is a thickness of the slag remained in the converter.
As a result, if the U-shaped passage is constructed such that h.sub.1 and h.sub.2 satisfy the formula (1), it is possible to prevent the slag from flowing out of the U-shaped passage.
But, the above mentioned formula (1) is a conditional equation by taking into consideration only the static balance of the molten steel with the slag.